Self-Healing Membrane

ABSTRACT

The invention relates to a membrane that heals on its own after being damaged mechanically as well as a method for producing said membrane which is used for pneumatic structures featuring an internal operating pressure of 10 mbar to 500 mbar. The inventive membrane is provided with a plastic layer on the pressure side, said plastic layer being interspersed with blisters that have a diameter ranging from 10μ to 200μ.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a method for producing a membranewhich, following mechanical injury in the sense of a puncture or abullet hole or penetration wound with a small-caliber weapon, is capableof closing this injury without external intervention.

2. History of the Related Art

The present invention is concerned with pneumatic structures such ashave been known, for example, from the European Patent Specifications EP1 239 756, EP 1 210 489, the European Patent Applications EP 03 700 039and EP 03 764 875 and the international publication WO 2005/007991.

EP 1 239 756 discloses a pneumatic mattress or bench seat which requiresno horizontal support as underlay. It can quickly be made ready for useand can be stowed away again with little space requirement. Thearrangement of the supporting chambers can be configured in such amanner that the mattress itself is configured in the manner of asupporting structure.

EP 1 210 489 discloses a pneumatic structural element in the manner ofan inflatable tubular hollow body which can absorb without bucklingtensile and thrust forces which may arise. The structural elements caneasily be joined together to form more complex components such as roofsor bridges, which may be erected very rapidly.

EP 1 554 158 (EP 1 210 489) discloses an adaptive pneumatic seat andbackrest for vehicles and airplanes which, despite the given basicstructure of the air chambers, offers high seat comfort corresponding toconventional foam cushions and brings a discernible saving in weightcompared with these.

WO 2004/009400 (EP 03 764 875) discloses an adaptive pneumatic seat andbackrests for vehicles and airplanes which, despite the given basicstructure of the air chambers, offers high seat comfort corresponding toconventional foam cushions and brings a discernible saving in weightcompared with these and in addition, can be simply designed ontoexisting seat shell structures.

WO 2005/007991 discloses a pneumatic support. The structural element caneasily be joined together to form more complex components such as roofsor bridges which may be erected very rapidly. In addition, thestructural element can easily be joined to conventional existingbuilding constructions.

Among other things, such pneumatic structures have in common that theyweigh comparatively little, i.e. they are easily transportable sincetheir membrane takes up little space in the deflated state and can bestored and transported in a space-saving manner.

These pneumatic structures comprise on the one hand large-areastructures having areas of several hundred to several thousand squaremeters with small excess pressures of the order of magnitude of 10 to500 mbar, on the other hand small-volume and small-area structureshaving excess pressures of 50-200 mbar, as in the case of pneumaticseats for example.

In all these cases the escape of compressed gas, usually air, should beavoided in order to maintain said internal operating pressure at leastat the necessary minimum.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a method whereby amembrane used as an envelope in such said pneumatic structures can beprepared and processed in such a manner that a hole of said type in thismembrane closes without intervention.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the self-healing membrane of thepresent invention may be obtained by reference to the following DetailedDescription, when taken in conjunction with the accompanying drawings,wherein:

FIG. 1 illustrates a cross-section through a membrane produced accordingto the invention;

FIG. 2 illustrates a first type of injury;

FIG. 3 illustrates FIG. 2 after removal of the injurious object;

FIG. 4 illustrates the first type of injury on an enlarged scale;

FIG. 5 illustrates a second type of injury during the self-healingprocess;

FIG. 6 illustrates a plan view of a film to be applied to the layer;

FIG. 7 illustrates, in plain view, a variant of the process step of FIG.6;

FIG. 8 illustrates a cross-section of a second variant for the processstep according to FIG. 6.

DETAILED DESCRIPTION OF THE INVENTION

Reference is now made in detail to exemplary embodiments of the presentinvention illustrated in the accompanying drawings. Wherever possible,the same reference numerals are used throughout the drawings to refer tothe same or similar parts.

FIG. 1 shows a membrane as an envelope of a pneumatic structure, theairtight membrane is designated by the reference numeral 1. The membrane1 can be, for example, fabric made of polyester, nylon, fiberglass,aramides coated with a plastic such as PVC, PU, silicone or Teflon® butalso flexible films made of such materials if the tensile stresses whichoccur are within permissible material properties.

A thin layer 2 of a plastic containing a plurality of small gas bubbles3 is applied to the inside of this membrane 1 by means of one of theknown techniques, i.e., for example, by wiping, rolling or spraying.Polyurethane, for example, is used as the plastic here.

For example, PVC-coated polyester fabric from Duraskin® (Type III,Verseldag, Krefeld) was coated with different commercially availableclosed-pore polyurethane foams according to the manufacturer'sinstructions. The two-component polyurethane foam Polyfoam F5(Polyconform GmbH) proved to be particularly suitable here.

The aforementioned gas bubbles 3 located in the plastic of the layer 2can either be incorporated therein by a rapid mixing process of theplastic. However, they can also be formed by the polymerization processand then left in the plastic by omitting a vacuum treatment. Gas bubblesin the range of 10μ-200μ have proved successful for the desiredself-healing process of an injury to the membrane 1. (An arrangementcomprising a stereomicroscope (Olympus, SZX9) and connected digitalcamera (Olympus DP12, Japan) was advantageous for studying the membrane1 coated by the layer 2).

The membrane 1 was then polymerized at elevated pressure. However, thepolymerization parameters such as pressure and temperature can vary,being specific to the plastic. The elevated pressure, typically 2 bar,is important.

An excess pressure over 5 bar leads to a deterioration in theself-healing or repair capability compared with an excess pressure of 2bar, which lies in the range which is already attainable duringpolymerization without excess pressure. As has been mentioned, the bestself-healing results were achieved during polymerization at an excesspressure in the range of 2 bar. Polymerization in an excess pressurerange of 2 to 3 bar also yielded good results. Polymerization in theexcess pressure range of 0.5 to 4 bar still yields significantly betterresults compared with polymerization without excess pressure.

The improved reaction properties can be attributed to the elevatedinternal pressure of the foam cells or bubbles (3) and also toconformational or structural changes inside the foam which have apositive influence on the repair, i.e. sealing, behavior merely as aresult of a different arrangement of the material.

The repair behavior could also be further improved by determining theamount of plastic to be polymerized applied per unit area; betterresults in the self-healing or repair behavior were achieved with anamount of coating in the range of 1 to 2 g for an area of about 20 cm²(circular sample having a diameter of 5 cm) as compared with amounts ofcoating outside this range. A coating amount of 1.6 g proved to beparticularly advantageous. This corresponds to a quantity per 100 cm² of5 to 10 g or an optimal quantity of 8 g of coating material.

Finally, it has also proved favorable to store the coated membrane afterpolymerization or protect it from mechanical stressing, i.e. to delaythe time before the possible first injury. An improvement in the repaircapability of the coated membrane was already observed after a week,with eight weeks having proved to be particularly advantageous.

If the membrane 1 is injured by piercing with a pointed object, a holethus formed will close partly by itself as a result of the elasticproperties of the membrane 1 as shown in FIG. 2. A fissure 5 as shown inFIG. 3 remains.

FIG. 4 shows a section of the uppermost part of the fissure 5. Under theinfluence of the internal pressure of the gas bubbles or an internalstress of the layer 2, a part of the layer 2 is pushed into the fissure5 and is partially pressed therein by the escaping air; a process whichcan take seconds to minutes. The cross-section of the hole is therebyreduced and the leakage flow severely suppressed. Since the internalpressure can usually be maintained by external means such as compressorsor, at low internal pressures of pneumatic structures, by fans, and inaddition, this internal pressure is usually permanently monitored, thereis sufficient time for an intervention in the sense of a repair to theenvelope of the pneumatic structure.

For fissures 5 of small diameter, complete closure can occur merely as aresult of the subsequent pushing of the layer 2.

In the case of larger holes 4 or holes caused by blunt objects or byprojectiles from firearms, however, the self-healing effect describedwith reference to FIGS. 2 to 4 does not result in complete closure ofthe hole 4. With such an injury, the layer 2 is torn along a larger rimof a hole. In order to make self-healing possible even in said cases,pre-polymers in a suitable form, for example, are provided whichpolymerize on contact with air and the moisture contained therein.Typically, on contact with the moisture in the air, such polymers formbubbles which are drawn into the hole 4 and completely cure there.Moreover, since the structural forces are absorbed by the membrane, ahole in the membrane is not a weakening if the force flow is interruptedas a result of the lower strength of its filling. Alternatively,two-component plastics can also be used in a suitable form instead ofpre-polymers.

FIG. 5 shows a first exemplary embodiment of a second step of thisproduction method according to the invention. Here, a plurality ofmicrocapsules 6 are mixed into the material of the layer 2. Suchmicrocapsules typically having a diameter of about 100μ, contain, forexample, a monomer, others contain an accelerator and/or a catalyst foreffecting the polymerization of the monomer. The monomer can alsocontain a solvent in which a suitable gas is dissolved under pressure.Such techniques are known from plastics technology. In addition, suchmicrocapsules 6 can also contain a pre-polymer which preferably containsa solvent and a propellant gas dissolved therein under pressure. If suchmicrocapsules 6 are torn by an injury, a puncture or a penetrationwound, the contents of a plurality of microcapsules 6 escape at the rimof the hole, forming a foam 7 which now hardens under the influence ofthe catalysts or the air humidity and permanently closes the hole 4. Inthe case of textile-reinforced membranes 1, adhesion to the walls of thehole 4 also occurs if the plastic contained in the microcapsules 6 doesnot bind sealingly or only poorly binds to that of the layer 2 or thatof the membrane 1 since a plurality of textile fibers are exposed andthe plastic emerging from the microcapsules can adhere to their openends. Otherwise, the plastic of the membrane coating must be matched tothat of the layer 2. Naturally and optimally, said plastics are matchedto one another, and the sealing can thus be optimized.

FIG. 6 shows a plan view of a blister film 8 which either contains amonomer or, in a selected distribution, a monomer and a suitablepolymerization partner or a moisture-curing pre-polymer withaccelerator, in a plurality of blisters 9. The size of the blisters 9can be selected and adapted in a broad framework so that, in conjunctionwith the distances a between the blisters 9, this ensures that in theevent of injuries to the membrane which go beyond the self-healingcapability of the layer 7, a plurality of such blisters 6 are torn. Afoam then forms, as described for FIG. 5, which enters into the injuryand polymerizes there. A distance d>a is provided between the rows ofblisters 9 at said distances a, which allows the blister film to befastened to the layer 2 by gluing or welding.

Naturally, the blisters 9 can be produced in any suitable shape and thesurface coverage thereby optimized. The size of the blisters 9 can alsobe varied widely.

FIG. 7 shows a variant of the exemplary embodiment from, also in planview. Here, elongated blisters 10 are provided, for example, filled witha monomer. In a second position, on the back of the blister film 8,other blisters 11 are arranged coincidentally (shown with dotted rims).Naturally, the shapes can also be selected differently here and therespective size ratios of the blisters 10, 122 can be provideddifferently. It corresponds to the inventive idea to arrange theblisters 10, 11 such that if a blister 10 is injured, a blister 11 isalso injured so that a polymerizing plastic is formed and can penetrateinto a hole 4 and seal this. In this exemplary embodiment a strip d>acan also be provided to allow the blister film 8 to be glued or weldedto the layer 2, without injuring the blisters 10, 11.

An alternative to the method examples in FIGS. 6 and 7 is shown in FIG.8. Before the layer 2 is pressure-polymerised, a blister film 12 isapplied thereto which, compared to the blister films 8 alreadydescribed, additionally has a perforation extending into the surface,consisting of a plurality of small holes 13 which preferably have adiameter of 0.1 to 1.0 mm. The blisters 9 again, for example, containtwo components of a suitable plastic.

After applying the blister film 12, the polymerisation now takes placeunder pressure, as described for FIG. 1. The blister film 12 is fixed onthe layer 2 by partial penetration of the layer 2 into the perforation.

Although various embodiments of the method and apparatus of the presentinvention have been illustrated in the accompanying Drawings anddescribed in the foregoing Detailed Description, it will be understoodthat the invention is not limited to the embodiments disclosed, but iscapable of numerous rearrangements, modifications, and substitutionswithout departing from the spirit and scope of the invention as setforth in the foregoing specification and following claims.

1. A method of producing a self-healing membrane of the type forcompressed-gastight sealing of a pressurized pneumatic structure havingan excess pressure in the order of 10 to 500 mbar, the methodcomprising: applying a layer of a polymerizable plastic to a side facinga compressed gas of an envelope, the envelope comprising a gastightmembrane, and adapted to contain a compressed gas; polymerizing thelayer of polymerizable plastic under pressure; and wherein air or gasbubbles, suspended in the polymerizable plastic and formed as a resultof prior mixing of the polymerizable plastic, and/or formed by thepolymerizing step are not removed by a vacuum treatment.
 2. The methodaccording to claim 1, wherein the membrane is reinforced with a textilefabric and is made gastight by means of a plastic coating.
 3. The methodaccording to claim 1, wherein a plurality of microcapsules is added tothe polymerizable plastic before the step of polymerizing.
 4. The methodaccording to claim 3, wherein the microcapsules comprise amoisture-curing pre-polymer.
 5. The method according to claim 3, furthercomprising: a first plurality of microcapsules comprising a monomer; asecond plurality of microcapsules comprising an accelerator and/or acatalyst; and wherein the ratio of the first to the second plurality ofmicrocapsules is adapted to the plastic to be polymerized.
 6. The methodaccording to claim 1, wherein prior to the step of polymerizing, ablister film is applied to the layer of polymerizable plastic, said filmcomprising: a plurality of small holes disposed on a side facing awayfrom the layer a plurality of blisters, comprising: a first number ofblisters comprising a monomer; a second number of blisters comprising anaccelerator and/or a catalyst; and wherein the ratio of the first to thesecond number of blisters is adapted to the plastic to be polymerized.7. The method according to claim 3, wherein a blister film havingblisters is glued or welded to the layer, the blisters having a uniformdistance from one another.
 8. The method according to claim 7, whereinthe blisters contain a moisture-curing pre-polymer.
 9. The methodaccording to claim 7, wherein the blisters are arranged alternately onthe blister film and comprise two components of a two-component plastic.10. The method according to claim 7, wherein the blister film furthercomprises a first plurality of blisters and a second plurality ofblisters disposed on opposite sides of a central film, wherein the firstplurality of blisters comprise a monomer, the second plurality ofblisters comprise a second component of a two-component plastic, and thefirst and second plurality of blisters are arranged at least partlycoincidentally.
 11. The method according to claim 10, wherein the firstplurality of blisters are elongated and the second plurality of blistersare generally circular.
 12. The method according to claim 7, wherein,the blisters are arranged in rows, the rows having variable spacing withrespect to each other.
 13. The method according to claim 1, wherein thestep of polymerizing takes place at an excess pressure of approximately0.4 to 4 bar.
 14. The method according to claim 1, wherein thepolymerizable plastic is applied to the membrane in an amount ofapproximately 5 to 10 g per 100 cm² of membrane surface.
 15. The methodaccording to claim 1, further comprising the step of storing the coatedmembrane over a period of 1 to 8 weeks.
 16. A self-healing membrane ofthe type designed for gastight closure of a pneumatic structure with aninternal operating pressure of 10 to 500 mbar, the membrane comprising:a self-healing plastic layer disposed on an interior side of an envelopecomprising a gastight membrane; wherein the layer is permeated with gasbubbles having a diameter of about 10μ-200μ.
 17. The membrane accordingto claim 16, wherein the membrane is reinforced with a textile fabricand is made gastight by means of a further plastic coating.
 18. Themembrane according to claim 16, wherein the self-healing plastic layercomprises a plurality of microcapsules comprising a moisture-curingpre-polymer.
 19. The membrane according to claim 16, wherein theself-healing plastic layer comprises a plurality of microcapsules, themicrocapsules comprising: a first plurality of microcapsules comprisinga monomer; a second plurality of microcapsules comprising an acceleratorand/or a catalyst; wherein the ratio of the first to the second numberof microcapsules is adapted to the plastic to be polymerized.
 20. Themembrane according to claim 16, further comprising: a blister filmcomprising a plurality of small holes; wherein the blister film isapplied to the self-healing plastic layer; and wherein material of thepolymerizable plastic layer which has passed through the holes fixes thefilm on the plastic layer.
 21. The membrane according to claim 20,wherein the blisters contain a moisture-curing pre-polymer.
 22. Themembrane according to claim 21, further comprising: a first plurality ofblisters comprising a monomer; a second plurality of blisters comprisingan accelerator and/or a catalyst; and wherein the ratio of the first tothe second number of blisters (9) is adapted to the plastic to bepolymerized.
 23. A pneumatic structure with an internal operatingpressure of 10 to 500 mbar, the pneumatic structure having an envelopecomprising, the membrane comprising; a self-healing plastic layerdisposed on an interior side of an envelope comprising a gastightmembrane; wherein the layer is permeated with gas bubbles having adiameter of about 10μ-200μ.
 24. A transportable or storable pneumaticstructure comprising at least one folded-together, gastight envelopewhich can be inflated to an internal operating pressure of 10 to 500mbar in the operating state, the envelope comprising a membrane, themembrane comprising: a self-healing plastic layer disposed on aninterior side of an envelope comprising a gastight membrane; wherein thelayer is permeated with gas bubbles having a diameter of about 10μ-200μ.25. The membrane according to claim 23, wherein the membrane isreinforced with a textile fabric and is made gastight by means of afurther plastic coating.
 26. The membrane according to claim 23, whereinthe self-healing plastic layer comprises a plurality of microcapsulescomprising a moisture-curing pre-polymer.
 27. The membrane according toclaim 23, wherein the self-healing plastic layer comprises a pluralityof microcapsules the microcapsules comprising: a first plurality ofmicrocapsules comprising a monomer; a second plurality of microcapsulescomprising an accelerator and/or a catalyst; wherein the ratio of thefirst to the second number of microcapsules is adapted to the plastic tobe polymerized.
 28. The membrane according to claim 23, furthercomprising: a blister film comprising a plurality of small holes;wherein the blister film is applied to the self-healing plastic layer;and wherein material of the polymerizable plastic layer which has passedthrough the holes fixes the film on the plastic layer.
 29. The membraneaccording to claim 28, wherein the blisters contain a moisture-curingpre-polymer.
 30. The membrane according to claim 29, further comprising:a first plurality of blisters comprising a monomer; a second pluralityof blisters comprising an accelerator and/or a catalyst; and wherein theratio of the first to the second number of blisters is adapted to theplastic to be polymerized.
 31. The membrane according to claim 24,wherein the membrane is reinforced with a textile fabric and is madegastight by means of a further plastic coating.
 32. The membraneaccording to claim 24, wherein the self-healing plastic layer comprisesa plurality of microcapsules comprising a moisture-curing pre-polymer.33. The membrane according to claim 24, wherein the self-healing plasticlayer comprises a plurality of microcapsules the microcapsulescomprising: a first plurality of microcapsules comprising a monomer; asecond plurality of microcapsules comprising an accelerator and/or acatalyst; wherein the ratio of the first to the second number ofmicrocapsules is adapted to the plastic to be polymerized.
 34. Themembrane according to claim 24, further comprising: a blister filmcomprising a plurality of small holes; wherein the blister film isapplied to the self-healing plastic layer; and wherein material of thepolymerizable plastic layer which has passed through the holes fixes thefilm on the plastic layer.
 35. The membrane according to claim 34,wherein the blisters contain a moisture-curing pre-polymer.
 36. Themembrane according to claim 35, further comprising: a first plurality ofblisters comprising a monomer; a second plurality of blisters comprisingan accelerator and/or a catalyst; and wherein the ratio of the first tothe second number of blisters is adapted to the plastic to bepolymerized.